Typically, series loop circuits consist of a plurality of power driven components connected in series with one another, and in series with a power source through a power line. In such series loop circuits, the failure of one power driven component can result in a complete shut down of the entire series loop. Thus, a break in the power line segments between components or a failure of a given component in the loop will result in a loss of power to all of the components in the loop.
An exemplary use of a series loop circuit is in an airport or taxiway lighting system. In such a system, each power driven component includes an isolation transformer and a lighting fixture. The isolation transformer has a primary side connected in series with the power line and a secondary side connected with the lighting fixture. Power from a power source is supplied to each component through the primary side of its respective isolation transformer, and all the components in the series loop circuit have their transformer primary sides connected in series. Typically, when the primary side of an isolation transformer or its connectors, fails, power to the remainder of the power driven components is cut off.
Series loop circuit arrangements and installations in this field of use as are presently known have a number of disadvantages. First, the failure of one primary circuit component will shut down the entire loop system. Second, when such loop circuits shut down, determination of the location of the system fault is most difficult. Third, replacement or repair of faulty system primary circuit components, once located, without interrupting the supply of power to the remaining components of the loop, is difficult if not impossible. Fourth, preventive maintaintance and determination of repairs required in short sections of the underground system is most difficult.
Thus, in a conventional series loop circuit system, maintenance is both time consuming and costly. When such a system breaks down, discovery of the system fault, or routine maintenance, is difficult to carry out without prolonged interruption of power to the entire system. In addition since the maintainance procedure is most difficult, the repairs of the system have not been made on the highest quality level, and the gradual deterioration of the system is very likely and the reliability and maintainability of the system over a period of time and prematurely has declined significantly.